Amazing work, I was lucky enough to get a decent HT when we built 2yrs ago but it's a fairly simple room, no decoration, doesn't matter when the light go out though.
Hopefully one day if we do it all again I'll be able to do something similar to yours, very inspiring.
So onto the window graphics, I'm a designer at a print company so I've a bit of experience with similar stuff. I'm assuming the highest quality source images you have are 1080p screen shots from the Blurays? I'd be hunting for something higher quality like a poster or book although using them is getting into grey area. Having said all that, I think you'd be surprised how big you can go even with a low res source. It's all about viewable distance, because they're so big, you will be viewing them from further away in order to take it all in so you can get away with something that is not ideal. Obviously up close you won't have the detail but you gotta work with what you've got.
By default Photoshop uses a Bicubic resize but there are other resizing methods (plugins or standalone applications) which can attempt to interpolate more detail into a scaled up image. This will only get you so far, then what I like to do to get rid of any hard pixelisation is to add a significant amount of noise before blurring the image to try and simulate film grain. It looks softer & more pleasing up close, the noise suggests detail & texture that the original is missing.
If the results look promising on screen then it's a good idea to crop a section out & do a cheap full size test print, hang it in situ & see if it works. I'm really curious how far a 1080p image can be used now so I might run some tests at work tomorrow & let you know.